1. Field of the Invention
This invention relates to underreamers used to open a hole below a restriction so that the opened hole is larger than the restriction itself. More particularly, this invention relates to a hydraulically actuated underreamer in cooperation with an actuator associated therewith to remotely actuate the underreamer when fluid is circulating in a borehole. The cutter arms of the underreamer retract when fluid circulation ceases through a cutter arm retractor contained within the underreamer housing.
2. Description of the Related Art
Underreamers are used in the petroleum industry to enlarge boreholes. Such tools can be used in drilling oil, gas or water wells and in mining operations. An underreamer has basically two operative states, a closed or collapsed state where the diameter of the tool is sufficiently small to allow movement of the tool in the narrowest part of the borehole, and an open or partly expanded state where one or more arms with cutters on the ends thereof, pivot out from the body of the tool. In this latter position the borehole is enlarged as the tool is rotated and lowered in the borehole.
A drilling type underreamer is typically used in conjunction with a drill bit positioned below or downstream of the underreamer. The drill bit can drill the borehole to be underreamed at the same time as the underreamer enlarges the borehole formed by the bit. Circulation of drilling fluid to the drill bit is required to remove detritus from the bottom of the borehole and to cool and clean the bit as it drills the borehole.
Underreamers of this type usually have hinged arms with cutters attached thereto. These pivoted arms tend to break during the drilling operation and must be removed or xe2x80x9cfishedxe2x80x9d out of the borehole before the drilling operation can continue. The tool typically has rotary cutter pocket recesses formed in the body where the arms are retracted when the tool is in a closed state. These pockets have a tendency to fill with debris from the drilling operation which makes collapsing of the arms difficult. If the arms do not fully collapse, the drill string may easily hang up in the borehole when an attempt is made to remove the string from the borehole. Most of the prior art underreamers utilize swing out cutter arms that are pivoted at an end opposite the cutting end of the reamer and are actuated by mechanical or hydraulic forces acting on the arms to extend or retract them. Typical examples of these types of underreamers are found in U.S. Pat. Nos. 3,224,507; 3,425,500 and 4,055,226.
An early example of a mechanically actuated expandable drill bit that does not use pivoting cutter arms to ream a borehole is taught in U.S. Pat. No. 3,365,010. This drill bit utilizes a pair of blade type cutters that ride in opposed, axially oriented channels. The channels are angled with respect to the axis of the bit such that when the blades impact the bottom of the borehole, shear pins retaining the blades are broken allowing the blades to move up the channels thereby expanding out against the borehole wall for subsequent borehole enlargement. A large pin for each blade retains the expanded blades in a desired position thus controlling the gage of the borehole. When the expandable drill bit is tripped out of the borehole, the blades fall down the angled tracks through frictional and gravitational forces thus diminishing the gage diameter of the expandable drill bit so that the drill string may be removed from the borehole. Once the shear pins are sheared, the expandable drill bit can only be used as a hole opener and only when the expandable drill bit is in contact with the borehole bottom.
U.S. Pat. No. 3,433,313 teaches an under-reaming tool having a tubular body with a sleeve movably positioned therein and adapted, when moved in one direction responsive to the pressure of drilling fluid, to move cutters to their opposite direction. Also responsive to the pressure of drilling fluid, the cutters are allowed to retract from their cutting position. A drilling fluid passage is formed in the tubular body to increase the flow area for drilling fluid when the cutters are in their cutting position and a means of positively moving the sleeve in the opposite direction with a wireline tool. The wireline tool is used to stop the flow of drilling fluid thus allowing the cutters to retract. This patent is disadvantaged in that a wireline device must be used to retract the cutters so that the tool may be tripped out of the borehole or to render the under-reamer inoperative downhole.
U.S. Pat. No. 5,368,114 teaches an under-reaming tool for use in preferably horizontal and extended reach boreholes. The tool includes a succession of stabilizers, underreamers and expandable stabilizers. A drilling mud activator is provided for the expandable elements of the underreamers and expandable stabilizers. The underreaming device comprises a main body with a number of guiding surfaces distributed over the circumference thereof which have a pitch angle that increases radially in an axial direction. A ring collar formed as a piston in a surrounding cylinder housing forms a small and a large radial annular surface. The piston further forms reaming pads/wings and/or stabilizer pads/wings in sliding contact with a respective guiding surface, the pads being taken up in ports in a jacket surrounding the main body in such a way that the pads can only be moved radially relative to the jacket, the jacket being attached to or formed as a part of the cylindrical housing. This patent is disadvantaged in that, in order to position the pad/wings associated with the reamer and stabilizer function, the pressure differential across the manipulating piston must be controlled and monitored by a microprocessor device positioned downhole; the information being electronically relayed to the rig platform.
Other related underreamer type patents include U.S. Pat. Nos. 4,141,421 and 4,889,197.
In general, prior art underreamers are disadvantaged in that those having cutting structures located at the end or near the end of a pivotable arm are inherently vulnerable to breakage of the pivot pins which retain the arms on the mandrel. Also, the mandrel recesses into which the cutters retract when they are collapsed tend to become easily fouled with debris during the cutting operation when the arms are extended. As a result, the arms are difficult to retract into the mandrel recesses.
Moreover, if the prior art tools are capable of transmitting fluid therethrough, it is typically accomplished using a centrally located hole or cylindrical tube. Most often, three cutters are used to dress each tool. A majority of these type tools do not positively collapse. Rather, a cutter retraction spring forces a piston to retract. The cutters however are not generally connected to the piston retraction spring and must retract through release of engagement with the borehole wall or retract through gravitational forces. The piston is usually in such a position that it is not possible to isolate fluid pressure from acting on it without preventing circulation of the drilling fluid. In other words, the tool cannot be enabled or disabled without stopping fluid circulation.
Another disadvantage of the prior art is that the cutter size and positioning are not optimized for the full range of hole opening sizes. In order to adjust the expanded diameter of a conventional underreamer, it is necessary to replace the cutting arms with larger or smaller arms or to adjust the location of their pivot points inwardly or outwardly with respect to the axis of the tool. It may even be necessary to replace the underreamer altogether with one which will provide a different expanded diameter.
Yet another disadvantage of the prior art is that the hydraulic capability is not optimized for the high fluid flow rates required.
The present invention overcomes the deficiencies of the prior art.
An expandable underreamer is disclosed which consists of an underreamer body forming at least a pair of opposed downwardly and inwardly angled slots. A means is provided to circulate fluid through the underreamer body and a means is also provided for connection to a drill string. At least a pair of cutter assemblies housed within the underreamer body is adapted to engage in the opposed angled slots formed by the underreamer body. Each cutter assembly consists of a cutter support body forming track engaging means at a first end, a piston drive means at a second end of the support body and underreaming cutter means formed therebetween. The piston is slidably engaged with a sleeve formed in the underreamer body; the sleeve being parallel with the angled slots formed in the underreamer body. The sleeve further is in fluid communication with a control port formed in the underreamer body. Fluid under pressure, when admitted to the piston sleeve below the piston drives the cutter assembly upwardly and outwardly along the angled slots to commence an underreaming operation. Spring means is additionally provided in the underreamer body to retract the cutter assemblies when fluid is shut off at the control port.
The hydraulically operated underreamer opens a borehole below a restriction that is larger than the restriction itself. The underreamer has a cutter system with a pair of cutters that engage the formation by traversing upward and outward along a track that is angled with respect to an axis of the underreamer body. The force pushing the cutters to the extended position is supplied by a piston built into each cutter support. The cutters may be actuated by a single piston acting on both the cutter support assemblies. Pressure acting on these pistons/piston comes from the pressure differential between the annulus and the drill string during circulation of the drilling fluid.
The cutters are supported on both sides of their cutting structure and are maintained in sliding contact with the underreamer body. The support arrangements on each side of the cutting structure also serve as guides for movement of the cutter assemblies with respect to the underreamer body. A spring opposes the upward and outward motion of the cutter systems and returns the cutters to the collapsed position in the absence of differential pressure (hydraulic pumps off).
An adjustment mechanism is used to set the stroke of the cutter system thereby determining the hole opening diameter.
The body of the underreamer tool incorporates by-pass ports for transmitting drilling fluid through to the remainder of the of the bottom hole drilling assembly. The bottom hole assembly could consist of mud motors, drill bits, MWD, etc.
The underreamer also contains a flow passage between the mud flow and the piston chamber that, when closed will disable the tool (it will not extend the cutters and no fluid will go through the underreamer nozzles). This feature enables the user to drill and underream simultaneously or to drill only if a hydraulic control device is incorporated with the underreamer.
The underreamer tool of the present invention utilizes by-pass ports to transmit drilling fluid through the housing of the tool. The fluid does not travel through the actuating piston to flow through the tool.
Further the underreamer uses only two cutters that enables the structure to be very strong and provides larger, more robust cutters than comparable prior art tools of approximately the same size. The two cutter configuration also allows for maximum support of the cutting structure within the body of the tool.
Still further the underreamer utilizes a pair of cutters without the conventional hinge pin associated therewith. Thus, the port area through the tool can be increased. Hence, the flow rate through the tool is substantially doubled.
An advantage of the present invention over the prior art is that the underreamer mechanism is built such that the cutters are forced to the collapsed position by a spring when there is insufficient pressure to overcome the spring force (pumps off).
Another advantage of the present invention over the prior art is that the tool utilizes fluid bypass ports to transmit fluid there through. The fluid does not travel through the piston to pass through the tool.
Still another advantage of the present invention over the prior art is the use of two cutters which enables the structure to be very strong (larger than comparable tools of the same size). The two cutter configuration of the present invention allows for maximum support of the cutting structure within the body of the underreamer tool.
Yet another advantage of the present invention over the prior art is by utilizing the two cutter design and eliminating the conventional hinge pin designs, the port area may be increased through the tool body. The allowable fluid flow rate through the present design is substantially doubled.
The above noted objects and advantages of the present invention will be more fully understood upon a study of the following description in conjunction with the detailed drawings.